Solid ink printers use ink in solid form, melt it and then transfer it in liquid form to a printhead. During power cycles, the ink will change phases from solid to liquid to solid, etc., and this generally occurs multiple times during its residence in the printer. This freeze/thaw cycle leaves air bubbles in the system that the system needs to purge, as air bubbles can cause the jets to fail.
Purging generally involves using air pressure to ‘clear’ the ink lines and conduits and results in both air and waste ink leaving the system. The volume of air leaving the system corresponds to the volume of ink leaving the system. In current applications, the systems generally purge the air through the jets or nozzles used to transfer the ink from the reservoirs to the printing substrate at the ‘downstream’ end of the ink path. The largest air bubbles that lie the farthest upstream typically require the largest volumes of ink to purge the bubbles since all of the ink in front of the air bubbles must be purged to clear the air bubble even with perfect efficiency. This results in a large volume of waste ink.
As printers move towards a more compact architecture, the removal of bubbles becomes even more inefficient.